Earth

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Earths Revolution and SeasonsDo not write what
is in GREEN
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Definition

• Revolution The movement of Earth in its orbit
  around the sun

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Evidence of Revolution

• Positions of constellations in the sky appear to
  move as the Earth rotates (daily-gtrise and set)
  and revolves (seasonally-gt ex. Only see Orion in
  the winter)

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Parallax-REVIEW (do not write)

• The apparent shift in position of the stars
• Cannot be detected with eye, but can be measured
  with precise instruments
• Proof of Earths revolution

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• Hold a pencil at arms length
• Cover one eye
• See what happens when you switch eyes but keep
  the pencil still
• Viewing the pencil from two different position
  produces the same shift as seen in nearby stars

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Earths Movement

• The Earth revolves counterclockwise when viewed
  from the North Pole.
• Earths orbit is an ellipse, which is a stretched
  out circle

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• The distance between Earth and the sun changes
  throughout the year
• The average distance is about 93 million miles

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Perihelion vs. Aphelion

• Perihelion (January 2) Closest to the sun (about
  91 million miles)
• Aphelion (July 4) Farthest from the sun (about
  95 million miles)

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How Much Time?

• Earth revolves once every 365.24 days
• Since an ellipse is 360 degrees total, each day
  we revolve about 1 degree

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Effects of Revolution

• Changes in the seasons and variation in the
  length of days and night

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The Reason for the Seasons

• The tilt of Earths axis and revolution causes
  the seasons

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• The hemisphere of the Earth that is pointed
  toward the sun receives more direct sunlight and
  has longer days, therefore, it has warmer
  temperatures

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• The hemisphere tilted away has shorter days and
  receives less direct sunlight, and is therefore
  colder

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Winter Solstice

• Typically 12/21
• Start of winter
• Shortest day of the year when the sun follows its
  lowest and shortest path across the sky.

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• The sun is over the Tropic of Capricorn (23.5
  degrees South)
• Points north of the Arctic Circle have 24 hours
  of darkness, and points south of the Antarctic
  Circle have 24 hours of daylight

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Summer Solstice

• Typically June 21
• Start of summer
• Longest day of the year

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• Path of sun in the sky is longer and higher than
  at any other time
• Sun is over the Tropic of Cancer (23.5 degrees
  North)

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The Equinoxes

• Vernal (Spring) and Autumnal (Fall)
• Typically occur March 21 and September 22

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• Sun is over the equator
• All points all over the world have about 12 hours
  of daylight and 12 hours of night

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Rotation vs. Revolution

• Rotation

• Revolution

• Movement of Earth around the sun
• Once a year
• 1 degree of orbit/day
• Causes seasons and length of day/night
• Proof Parallax (apparent movement of the stars)

• Movement of Earth around its axis
• Once a day
• 15 degrees longitude/hour
• Causes night and day
• Proof Foucault's Pendulum and Coriolis Effect